The Imaging Core has two major objectives. The first is to define the anatomical distribution and time course of the CNS effect of HIV-1 infection. A second important objective is to detect and monitor opportunistic infections in the CNS. In the previous funding period we have studied 505 subjects in the Imaging Core. We have established that abnormal findings detectable on clinical MR exams occur infrequently in neurologically-normal HIV+subjects, and then primarily in patients with AIDS. Our clinical research ratings have shown, however, that HIV+subjects more frequently worsen on MRI than do their controls, and the abnormal findings are correlated with other markers for progression of the disease. Our MR morphometry studies suggest that volume loss occurs in gray matter structures, even during the medically asymptomatic stages of the illness, although antiretroviral medication appears to retard this loss. Studies of post-mortem MRI examinations in AIDS patients suggest that volume losses measurable on MRI are correlated with the distribution of viral burden (gp41) in the brain. A major undertaking of the Imaging Core for the next funding period will be to establish stronger links between the brain structural changes observable in vivo using MRI volumetric technique and the findings at autopsy and to relate these to specific neurocognitive changes. To this end, careful correlation of data from repeated MR examinations with post-mortem findings will be performed. Thus, particular emphasis will be placed in all in vivo MRI exams (and the post-mortem MRI exams) available for cases entering the Neuropathology Core. In the service of the stated objectives the Imaging Core will perform the following functions: 1. Collection of a longitudinal MRI database (biannual exams for all subjects except AIDS subjects, who will receive semiannual exams). 2. Compilation and analysis of research ratings of all MR exams. 3. Clinical follow-up and database tagging of all opportunistic CNS infections detected on MRI. 4. Post-mortem MRI examination of the formalin-fixed left hemispheres of cases (without opportunistic infections) entering the Neuropathology Core. 5. Quantitative Image Analysis: Anatomical analysis of all in vivo MRI exams and a post-mortem MRI exam for all Neuropathology Core cases without opportunistic infections of the CNS (cases with CMV will be included). Anatomical analysis of images for MR Information Processing Project. Development and application of region-of- interest analysis for functional MR image datasets. Image registration and development of region-of-interest analysis for SPECT studies.